I was given a 180 with it when my roof was done and as far as I can recall it is on all the time. It tweets at you when someone comes along side. Slightly unnerving.
My 2013 Cali has it, a light on door mirrors lights if there's a vehicle coming passed in either inside or offside lane. It does seem to have a pretty long range. Not sure I would bother with paying for it as an option but it's a nice toy!